Pump jets are known to offer several advantages over propellers in use with marine drives. For instance, the shrouded construction of pump jets significantly reduces the risk of injury to marine life and divers, relative to propellers. Additionally, pump jets generate a more concentrated, directional thrust. Because of these and other advantages, it is known to retrofit propeller-driven marine drives with pump jets.
Referring to FIG. 1, a typical marine drive 110, such as an outboard motor, includes an engine 112, a drive shaft 114, a gear housing 116, a propeller shaft 118 and a propeller 120. The engine 112 turns the drive shaft 114. Through gear housing 116, the rotational motion of the drive shaft 114 is transferred to the propeller shaft 118 and the propeller 120.
Referring to FIG. 2, the propeller shaft 118 and propeller 120 rotate about a shaft axis 124. The propeller shaft 118 extends through a propeller shaft passage 126 defined within the propeller 120. A thrust bushing 28 is arranged between the propeller 120 and an axial end face 130 of the gear housing 116. A retention nut 132 holds the propeller 120 onto the propeller shaft 118. As will be appreciated, the propeller 120 can be removed by removing the retention nut 132 and sliding the propeller 120 off the shaft 118.
Referring to FIG. 3, with the propeller 120 removed, a pump jet assembly 140 can be retrofit to the marine drive. The pump jet assembly 140 includes a shroud 142 and a rotor 144. The shroud 142 surrounds the rotor 144, directing water flow thereto and channeling water flow therefrom.
The shroud 142 can be divided into a front shroud portion 146 and a rear shroud portion 148, which are detachably connected. The front shroud portion 146 includes a plurality of forward stationary vanes 150, extending radially between the front shroud portion 146 and the gear housing 116. The rear shroud portion 148 includes a plurality of rear stationary vanes 158 extending radially between the rear shroud portion 148 and a stator hub 160. The rear stationary vanes 158 and the stator hub 160 are collectively referred to as the stator and direct water flow passing through the rear axial end 162 of the shroud 142.
The rotor 144 includes a central hub 164 with a plurality of rotor blades 166 extending radially outward therefrom. The rotor 144 is mounted substantially coaxially with the propeller shaft 118. The nut 132 holds the rotor 144 onto the shaft 118.
An exhaust block/duct adapter 184 is arranged above the gear housing 116. The exhaust block/duct adapter 184 blocks the normal outboard motor exhaust path which routes exhaust gas out the gear housing 116, where it would be dispersed by the propeller 116. Instead, the adapter 184 allows the exhaust gases to be channeled to an exhaust duct 186, preventing cavitation of the pump jet assembly 140 due to exhaust gases passing through the shroud 142.